Preheat your oven to 425°F and grease a 9x13 inch baking dish. In a bowl, combine the softened butter, 1 1/4 cups flour, and 1 1/2 tablespoons sugar until the mixture resembles coarse breadcrumbs. Press this mixture firmly and evenly into the bottom of your prepared dish to create an even crust layer. This creates a tender shortbread-like foundation that will bake partially before the filling is added.

Place the crust in the oven and bake for 10 minutes until lightly golden. While the crust bakes, prepare your rhubarb filling by combining 1 cup granulated sugar, 1/4 cup flour, and 1/4 teaspoon salt in a bowl, then fold in the sliced rhubarb until evenly coated. I like to toss the rhubarb gently rather than stirring vigorously—this keeps the pieces intact and prevents them from releasing too much juice too early. When the crust is done, remove it from the oven and reduce the oven temperature to 350°F.

Spread the rhubarb mixture evenly over the partially baked crust from Step 1. In a separate bowl, beat the room-temperature cream cheese with 0.5 cup sugar until smooth and creamy, then add the egg and vanilla extract, beating until just combined. Gently spread this cheesecake mixture over the rhubarb layer. The room-temperature cream cheese is important here—it blends smoothly without lumps and creates a silkier filling than cold cheese would.

Bake the bars at 350°F for 35 minutes until the cheesecake layer is set but still has a slight jiggle in the center. While the bars finish baking, whisk together the sour cream and 1 tablespoon sugar in a small bowl until smooth. Remove the bars from the oven and immediately spread the sour cream mixture evenly over the hot cheesecake layer—the warmth helps it meld slightly with the filling, creating a cohesive topping.

Allow the bars to cool completely at room temperature for at least 2 hours before cutting and serving. This cooling time is essential for the layers to set properly and for the flavors to meld together beautifully. For the cleanest cuts, refrigerate for an additional hour or two and use a sharp knife dipped in hot water between cuts.